HOUSTON, Dec 19 (Reuters) - Shell was flaring on Monday atits 156,400 barrel per day Martinez refinery near San Francisco,California, a local fire official said by phone.
Flaring typically occurs when restarting or shutting down aunit for maintenance, or where there is an unplannedinterruption to refinery operations.
It was not clear what led to Monday's flaring at the Shellrefinery.
A company representative did not immediately respond to arequest for comment. (Reporting by Liz Hampton; Editing by Meredith Mazzilli)